Electrophotographic developing device

ABSTRACT

An electrophoretic developing device having an inclined conductive surface with a clamping means provided near the top of said surface for an electrophotosensitive sheet opposite to said surface. A liquid developer is intermittently supplied from a suitable feed means so as to provide a film of liquid between the conductive surface and the sheet.

United States Patent 1 1 3,566,834

[72] lnventors Yasuo Tamai; [56) References Cited Satnru Honjo; Seiji Matsumoto; Masamichi UNlTED STATES PATENTS 2 859 127 11/1958 Matthews ll8/637X [211 1968 2,918,900 12/1959 Carlson 118/637 [22] Sew-1 2,952,241 6 9/1960 Clark m1. 118/637(C) [45] Patented Ma l 2, l 1 L d 3,001,888 9/1961 Metcalfe et al..... 117/37(LX) [731 Asslgnee 3,079,890 3/1963 Oliphant 117/37(L)X 3,284,224 11/1966 Lehmann l18/637(L)X 3,416,493 12/1968 Robinson et al. 117/37(L)X Primary Examiner-M0rris Kaplan 54] ELECTROPHOTOGRAPHIC DEVELOPING Attorney-Sughrue, Rothwell, Mion, Zinn & MacPeak DEVICE 3 Clams 8 Drawing Flgs' ABSTRACT: An electrophoretic developing device having an [52] U.S. Cl. 118/637 inclined conductive surface with a clamping means provided [51] Int. CL... B05b 5/00 near the top of said surface for an electrophotosensitive sheet [50] Field of Search 118/637, opposite to said surface. A liquid developer is intermittently 638, 629, 636, 637 (LX), (Miscellaneous); ll7/37CX, 17.5; 95/(lnquired) supplied from a suitable feed means so as to provide a film of liquid between the conductive surface and the sheet.

PATENTED MAR 2 I971 SHEET 2 UF 2 S M T N E v N ELECTROPI-IOTOGRAPHICDEVELOPING DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic liquid developing device suitable for the reproduction of continuous gradation.

2. Description of the Prior Art Many techniques for developing an electrostatic latent image formed on an electrophotographic material have been disclosed in the prior art. Among the more common techniques are included magnetic brush, cascade, powder cloud and liquid developing processes. Of these processes, powder cloud and liquid developing processes are known to be especially suitable for reproducing continuous gradation. Developing by the powder cloud process however involves several severe problems, for instance, the powder cloud developing device must be small in size and must be capable of exact operation and the speed of developing must be maintained relatively constant. On theother hand, the liquid developing process has a number of advantages in that the apparatus used in that process can be operated simply and with high developing speed. Moreover, the liquid developing process can be used for the reproducing continuous gradations because the toner which is suspended in the liquid developer can be decreased in particle diameter. This latter type of developing apparatus has one major disadvantage, however, in that it cannot be simply constructed. For this reason, liquid developing devices have been used extensively only to reproduce line images. The complexity of the liquid developing devices is due to the fact that a critically small interval must be maintained between the surface to be developed and the developing electrode, such that when reproducing a wide image area having a uniform density, it is necessary to place the developing electrode at a very small distance from the latent image bearing surface and to carry out the process slowly while feeding a sufficient quantity of liquid developer into this gap. When reproducing continuous gradations, it is necessary to use as the developing surface an electrophotographic sensitive material which has a very long dark potential decay time in the liquid developer, a developing electrode, and a liquid developer having a very high electric resistance and a very low dielectric constant, and the processing time must be reasonably extended. However, in order to align a wide developing surface in opposition to a sufficiently large developing electrodearea while maintaining the very slim gap between the surface and the electrode, a means must be provided for supplying fresh liquid developer into the gap so that the flow of the developer will not destroy the toner image. While several solutions to thisproblem have been suggested, none of them have heretofore proved successful. In U.S. Pat. No. 3,256,855 and in U.S. Pat. No. 3,203,395, a method is disclosed whereby the developing electrode is insufficient making it difficult to treat a large surface over a sufficiently slow period. U.S. Pat. No. 3,079,890, due to the absence of a developing electrode, shows it is difficult to reproduce a continuous-tone image with the desired high fidelity. There is also a short-coming trail which appears near the toner image in the direction of the flow of the liquid developer.

While a wire-gauZe-type developing electrode might be used to resolve this problem, ingenious contrivance is required to maintain the slim interval between the wire-gauze-type developing electrode and the surface to be developed. In addition, another critical problem is that a fine meshy disturbance is often apt to show up in the image. Accordingly, it is not preferable to use a flat metallic plate as the developing electrode unless the question of liquid developer supply is solved.

SUMMARY OF THE INVENTION It has now been found that where either the developing electrode or the electrophotographic sensitive surface is flexible and a thin layer of liquid developer is sandwiched therebetween, even if the developing electrode nearly touches the electrophotographic sensitive surface neither the electrostatic latent image area nor any part of the actual image will be adversely affected during the developing process, unless there is some movement between the developing electrode and the surface to be developed.

The present invention relates to a device having an inclined conductive surface, which serves as a developing electrode or which serves to carry the electrophotographic material. A clamping device is provided near the top of the surface which serves to clamp the top edge of an electrophotographic sheet material. A developer feeding means is provided to intermittently supply the liquid developer between the inclined surface and the sheet. When the inclined surface is the developing electrode, the clamping means clamps the top edge of the electrophotographic sensitive sheet such that the inclined conductive surface faces the latent electrostatic image of the sheet. When the incline plane serves merely to carry the electrophotographic material, the clamping means clamps the top edge of the flexible conductive sheet which then serves as the developing electrode. In either case, the liquid developer is fed intermittently between the surface bearing the latent image and the developing electrode. Developing occurs with the developing electrode while the electrode and latent image are in face-to-face relationship with each other with a thin layer of the liquid developer therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A and 1B are in vertical sectional views which illustrate one device which accomplishes the objects of this invention;

FIG. 2 is a perspective view of the device shown in FIG. 1;

FIGS. 3A and 3B are vertical sectional views which illustrate a modified device of that shown in FIG. 1;

FIG. 4 is a perspective view of the device shown in FIG. 3;

FIG. 5 is a perspective view showing the liquid developer circuit; and

FIG. 6 illustrates the means to feed the.liquid developer intermittently.

In FIG. 1, 1 is a conductive plate inclined at an angle 9 with respect to a horizontal level. A chamber 2 is provided near the top of said conductive plate 1, which is provided with a slit type jet port or a row of holes which permits feeding the liquid developer onto the surface of conductive plate 1 uniformly in its lateral direction. 4 is a valve which regulates theamount of the liquid developer fed to the system. An apron shaped part 5 is provided which retains the top edge of the electrophotographic sensitive sheet 6 to be developed. The surface of the sheet having the electrostatic latent image is placed face down on the plate. The chamber 2 is filled with the liquid developer and is replenished constantly. As shown in FIG. 1A, when the chamber 2 is lifted slightly, the valve 4 opens and simultaneously the apron part 5 widens the interval between the conductive plate 1 and the top edge of sheet 6, the liquid developer flows out of the jet port 3 and runs down between the conductive plate 1 and the sheet 6 along the conductive plate 1, lifting sheet 6. As illustrated in FIG. 18, when the chamber 2 is lowered, valve 4 closes by coming into contact with the conductive plate 1 and the supply of the liquid developer is interrupted. A thin layerof liquid developer is thereby provided between the conductive plate 1 and the sheet 6 which moistens both. The majority of the liquid developer will flow from the free edge at the lower end of the sheet. Accordingly, if the chamber 2 is moved up and down periodically to feed the liquid developer intermittently in between the conductive plate 1 and the sheet 6, the liquid developer will pulsate and fresh liquid developer will be constantly replenished. It has been experimentally found that when pulsating or flowing down, the liquid developer will scarcely be discharged from the side edge of the sheet 6, but will be discharged from the bottom edge. The latent electrostatic image on sheet 6 will be developed principally by the thin layer of liquid developer existing between sheet 6 and the inclined conductive plate 1. By providing a thin layer of liquid developer in sufficient quantities for developing a latent electrostatic image and by maintaining a small distance between the inclined conductive plate 1 which works as a developing electrode and the sheet 6 continuous gradations can be satisfactorily obtained.

FIG. 2 is an oblique view illustrating the developing liquid feed chamber 2 and its surroundings when the device of the present invention is in the condition as illustrated in FIG. 18. Pipe 21 is connected on the discharge side of the chamber 2 and is provided with a bend in order to apply sufficient static pressure to open valve 4 of the liquid developer. 9 is a pipe which supplies the liquid developer to chamber 2. If the device is so constructed that valve 4 opens automatically when chamber 2 is raised, bend 8 is not necessarily required. 22 and 22' are clips for clamping the top edge of sheet 6 to apron of chamber 2.

FIGS. 3 and 4 illustrate another embodiment similar to FIGS. 1 and 2. In FIG. 3, 1 denotes a conductive plate inclined at an angle 6 with respect to the horizontal and 2 denotes a chamber disposed in the neighborhood of the upper end of the conductive plate 1, said chamber being provided with an injection outlet 3 composed of either a slit or a row of orifices for supplying a substantially uniform layer of liquid developer to the upper surface of conductive plate 1. 4 denotes a valve for regulating the amount of liquid developer to be supplied. An electrophotographic sensitive material (hereinafter called sheet") is carried on the inclined conductive plate 1 with its surface to be developed facing upwardly. A flexible conductive thin plate 7 is provided for use as the developing electrode. An apron-shaped portion 5 of chamber 2 is positioned to hold the upper edge of the conductive thin plate 7. Chamber 2 is continuously filled with liquid developer. When chamber 2 is raised slightly as shown in FIG. 3A, valve 4 is opened and, at the same time, apron-shaped portion 5 acts to expand the interval between sheet 6, the upper edge of conductive plate 1, and the upper edge of the thin conductive plate 7. The liquid developer thereby flows from the injection outlet 3 and runs down along the surface to be developed between the sheet surface 6 and conductive thin plate 7 so as to force conductive thin plate 7 upward. When chamber 2 is lowered, as illustrated in FIG. 3B, valve 4 closes as it comes into contact with conductive plate 1 or sheet 6, and the supply of the liquid developer is discontinued. The liquid developer thereafter flows out through the free edge of the lower end of conductive thin plate 7, leaving a thin layer ofliquid developer in sufflcient quantity to moisten both the conductive thin plate 7 and the sheet 6. If chamber 2 is raised and then lowered periodically to intermittently supply liquid developer between the conductive thin plate 7 and the sheet 6, the liquid developer will flow pulsatively between each thereby supplying a fresh supply of liquid developer at all times. Experiments have shown that when the liquid developer flows down pulsatively, it will be discharged from the lower edge of the sheet and very little will run out from the sides of the sheet 6. The latent electrostatic image on sheet 6 is developed predominantly by the thin layer of liquid developer intervening between sheet 6 and conductive thin plate 7. Since this thin layer of liquid developer is in an amount sufficient for developing the electrostatic latent image and the conductive thin plate 7 acts as a developing electrode while sheet 6 is maintained between them with a very narrow space between them, the desired continuous tone can be reproduced satisfactorily.

FIG. 4 represents an oblique drawing intended to show the surroundings of chamber 2 which supplies the liquid developer when the device is held in the position shown in FIG. 3B. In order to apply the liquid developer a static pressure is provided which opens valve 4. A bend 8 in pipe 21 is provided on the discharge side of chamber 2. A pipe 9 for delivering liquid developer to chamber 2 is provided. Bend 8 is not required, however, when the device is of such construction that valve 4 can be automatically opened as chamber 2 is raised. 22 and 22 denote clips which serve to hold the upper edge of conductive thin plate 7 at the apron-shaped portion 5 of the chamber 2.

FIG. 5 illustrates one example of a device according to the present invention, which is equipped with a liquid developing feed chamber 2 as illustrated in FIG. 2 or FIG. 4. In this device 10 is a liquid developer tank, 11 a pump, 12 a motor, 13 a pipe for recovering used developer 10 and 14 are walls which are provided at the bottom and sides of inclined conductive plate 1. In this device, the liquid developer in tank 13 is supplied to chamber 2 by means of pump 11 driven by motor 12. The used liquid developer is collected from the free bottom end of the sheet and from the small quantity flowing from the sides of the sheet or the flexible conductive thin plate by pipe 13. The used developer is transported along the inclined conductive plate 1 and wall 14 and is recovered via pipe 13 into the liquid developing tank 10. Unused liquid developer is collected in the liquid developer tank 10 by pipe 21 via bend 8 which applies the proper amount of pressure to the liquid developer. In order to move the chamber 2 up and down, at least a part of pipes 9 and 21 should be flexible.

FIG. 6 illustrates a concrete example of a mechanism for intermittently feeding liquid developer between the developing electrode and the electrophotographic sensitive material by raising and lowering the chamber 2. A push rod 15 is fixed to pipe 21 on the liquid developer feed side of chamber 2. This push rod is raised and lowered by eccentric cam 20 which is rotated by the revolving shaft 17 of motor 16 provided beneath conductive plate 1 via speed change gears 18 and 19. An additional pair of the same mechanism may be provided on the other side of chamber 2 and moved by the same revolving shaft 17, so as to raise and lower chamber 2 periodically. By this up-and-down motion of chamber 2, valve 4 of chamber 2 closes and opens and the liquid developer is fed intermittently in between the electrophotographic sensitive material and the developing electrode.

In the device of the present invention, it is desirable that the inclination of the conductive plate 1 with respect to the horizontal be 530 when the liquid developer is of normal viscosity. If this inclination is too large, a toner image on the electrophotographic sensitive material is liable to be damaged by the flow of the liquid developer, producing streaks and spots, whereas if the inclination is too small, the flow velocity of the liquid developer is too low, making it impossible to feed a sufficient amount of liquid developer to enable the pulsating condition between the electrophotographic sensitive material and the developing electrode. Any suitable material can be used for preparing the conductive plate 1 but a metal plate is preferable. A synthetic resin plate having its surface glued onto a metallic film, or a synthetic resin plate having a metal vacuum evaporated or coated with a conductive paint may however also be employed. If it is desired to watch the progress of the developing process, a section of the flexible developing electrode in FIG. 1 or of the conductive plate in FIG. 2 may be replaced by a transparent conductive material such as Nesa glass, whereby the developing progress can be observed from behind the developing electrode or the conductive plate.

A developing time of IO sec.3 min. has been found to be quite suitable. If the developing time is too short, only a low density image affected by edge effect can be obtained. If the pulsating motion of the liquid developer is too rapid, a large quantity of the liquid developer will flow, thereby enlarging the distance between the electrophotographic sensitive material and the developing electrode disrupting the functioning of the developing electrode. If the flow velocity of the liquid developer is accelerated, stains will be produced in the flowing direction of the liquid developer. It is desirable therefore that the pulsating current be produced at the rates of one per second to one per 30 seconds.

According to the present invention, as described above, a sufficient amount of fresh liquid developer is supplied at a relatively low flow velocity while a small distance is maintained between the conductive plate, or the flexible conductive plate serving as the developing electrode, and the electrophotographic sensitive material, and therefore by this means continuous gradations can be reproduced satisfactorily without destroying the toner image on the surface being developed. This invention makes it unnecessary to use a spacer, etc. to maintain the small interval between the electrophotographic sensitive material and the developing electrode. Only a small quantity of liquid developer need be supplied between the electrophotographic sensitive material and the developing electrode. Furthermore, since the liquid developer need not be exposed to air, there is no problem of the toner being deteriorated by evaporation or by mixture with condensed moisture from the air as in many convention devices.

Since the liquid developer reaches only the surface of the electrostatic latent image on the electrophotographic sensitive material, the back of the material will in no way be stained.

Despite all the novel advantages of this invention, over conventional devices used for the same purpose, the device of the present invention can be operated simply and at a higher developing speed.

We claim:

1. An apparatus for developing an electrostatic latent image formed on an electrophotographic material, said apparatus comprising an inclined conductive surface, clamping means provided near the top of said conductive surface for clamping the top edge of a sheet material, a sheet material having the top edge thereof secured by said clamping means, a developer feeding chamber positioned near the top of said conductive plate and having an opening therein for supplying a liquid developer between said conductive surface and said sheet material, valve means secured to said opening of said chamber and means connected to said chamber for effecting periodic opening and closing of said valve such that the liquid developer is fed intermittently between said conductive plate and said sheet material.

2. The apparatus of claim 1 wherein said sheet material comprises a latent image containing electrophotographic sensitive paper, said latent image being in facing relationship with said inclined conductive surface whereby said conductive sur face acts as a developing electrode.

3. The apparatus of claim 1 wherein a latent image containing electrophotographic sensitive material is carried on the inclined conductive service, said latent image being in facing relationship with said sheet material, and wherein said sheet material comprising a flexible conductive thin plate whereby said conductive thin plate acts as a developing electrode. 

2. The apparatus of claim 1 wherein said sheet material comprises a latent image containing electrophotographic sensitive paper, said latent image being in facing relationship with said inclined conductive surface whereby said conductive surface acts as a developing electrode.
 3. The apparatus of claim 1 wherein a latent image containing electrophotographic sensitive material is carried on the inclined conductive service, said latent image being in facing relationship with said sheet material, and wherein said sheet material comprising a flexible conductive thin plate whereby said conductive thin plate acts as a developing electrode. 